The present invention relates to data communications and deals with a method and a device for operating a network. The present invention also refers to a network with a corresponding data telegram.
Communication systems are known in the related art. Distributed communication systems, in particular, are utilized in many technical applications. Distributed communication systems are used, e.g., in automation systems based on decentralized control and drive system engineering, in which a large number of individual systems are often controlled and driven in a temporally synchronized manner. An example of a single system of this type is a drive unit, e.g., with a synchronous or asynchronous motor used to drive one of many axes that function in a manner such that they are mutually interpolating or closely interconnected. Typical fields of application of automation systems of this type based on decentralized control and drive system engineering are printing presses or machine tools, and robotic systems with a large number of conveying and operative elements that operate in a synchronized manner.
Communication systems of this type include at least two, but usually many more participants, which are preferably configured and/or arranged in a hierarchical structure, with one participant being configured as the central participant and the remaining participants being configured and/or arranged as further participants in the communication system. A hierarchical architecture is known, e.g., as a master-slave structure with the central or main participant as the “master” or “master participant” (main station), and the further participants as “slaves” or “slave participants” (substations or secondary stations). The main participant is designed as the central participant that generates and sends control signals to the further participants. The further participants are in communication contact with the central participant to receive these control signals and to communicate further with the central participant, as necessary, and they are typically in communication contact with the other participants as well. The slave participants are usually process interfaces, such as sensors and actuators, i.e., input/output assemblies for analog and digital signals, and drives. Signal processing, with data preprocessing, must be decentralized among the slave participants to keep the quantity of data to be transmitted low. This requires that the master participant and the further slave participants communicate with each other. In this regard, three basic architectures (“topologies”) are known from the related art. The ring structure, in which a signal generated by the central participant travels around the ring and therefore passes each of the other participants in series.
The bus structure, with a central bus line to which the central participant and other participants are connected. The signal and data transfer is accomplished via a data bus in a known manner. When the central bus line has long paths, it is common to interconnect a “repeater” in the central bus line to amplify the signal. This is also practical with the ring structure, although the “repeater” is preferably realized within a participant in this case.
The third structure is a star architecture with a central switching participant (a “switch”) integrated in the connecting line. A signal generated by the central participant is relayed via the switch to the participant specified as the receiver.
The three topologies described can also be part of a more complex system in which a plurality of basic architecture designs are realized in an interconnected manner. In this case, one of the central participants or a superordinate central participant has the task of generating a superordinate control signal.
Distributed communication systems are also known from the related art, with which the master function can be transferred among a plurality of participants or even among all participants. A requirement of “multi-master” systems of this type is that a plurality of participants have the functionality of a central participant and that they exercise this functionality when a defined condition exists. In this process, a participant that previously served as a further participant becomes the central participant, and the previous central participant becomes the further participant in the communication system. A possible condition for a transfer of this type can be, e.g., the absence of a control signal from the previous central participant.
The applicant currently offers a distributed communication system with a ring-type structure on the market, called the SERCOS Interface® (SErial Real Time COmmunication System). This system generates and sends control signals via a central participant to further participants. The further participants are typically connected with the central participant via optical waveguides. The SERCOS Interface® specifies strictly hierarchical communication. Data are exchanged in the form of data blocks, the “telegrams” or “frames”, between the controller (master) and the substations (slaves) in temporally constant cycles. The further participants and/or substations do not communicate directly with each other. In addition, data contents are specified, i.e., the significance, depiction and functionality of the transmitted data are predefined to a significant extent. With the SERCOS Interface®, the connection of the controller with the ring is the master, and the connection of one or more substations (drives or I/O stations) is the slave. A plurality of rings can be linked to one controller, with the controller being responsible for coordinating the individual rings with each other. This is not specified by the SERCOS Interface®.
This communication system is used preferably for the closed-loop and open-loop control of distributed motors, e.g., synchronous or asynchronous motors. The further participants in the communication system are, therefore, the control devices for the closed-loop and open-loop control of a motor. The main applications for this communication system are, in particular, drives of machine tools, printing presses, operative machines, and machines used in general automation technology. With the SERCOS Interface® there are five different communication phases. The first four phases (phase 0 through phase 3) serve to initialize the participants, and the fifth phase (phase 4) is regular operation. Within one communication cycle, every substation exchanges data with the controller. Access to the ring is deterministic within collision-free transmission time slots. With the SERCOS Interface® there are three types of telegrams: Master Synchronization Telegrams, Amplifier Telegrams and Master Data Telegrams. Master Synchronization Telegrams (MST) are sent out by the master participant. They contain a short data field, are used to define the communication phase and serve as the “clock”. Amplifier Telegrams (AT) are sent by slave participants and include, e.g., actual values of a drive controlled by the particular slave participant. Master Data Telegrams (MDT) are “big picture” telegrams that contain data fields for all slave participants. The master uses Master Data Telegrams to transmit setpoint values to each slave. During initialization, every substation is notified of the start and length of its (sub-) data field. The SERCOS Interface® defines the following types of data, i.e., operating data, control and status information, and data transmitted in a non-cyclic manner. The operating data (process data) are transmitted in every cycle. Examples include setpoint values and actual values. The length of the operating data range is parameterizable. It is established during initialization and remains constant while the ring operates.
The control information transmitted by the master participants to the slave participants, and the status information sent by the slave participants to the master participants are release signals and “ready” messages, for example. Data transmitted in a non-cyclic manner (service channel) include setting parameters, diagnostic data and warnings. Command sequences are also controlled via this non-cyclic transmission. A communication cycle of the central participant is started via transmission of a MST. All communication-specific times are based on the end of this short telegram, which is approximately 25 μs in duration. The substations now send their Amplifier Telegrams (AT) in succession, in their respective transmission time slots. After the last AT, the master sends the MDT. The next cycle begins with another MST. The time interval between two MSTs is referred to as SERCOS cycle time.
With the SERCOS Interface®, communication is synchronized with the end of the MST. A synchronization telegram is generated by the central participant—preferably at equidistant intervals—and fed into the communication ring. In the closed-loop controllers, a time parameter typically links receipt of the synchronization telegram and the synchronization signal with the processing of setpoint/actual values, which results in a determination and allocation of open-loop and closed-loop parameters to the particular servo motors.
Since the secondary participants function as slaves and represent the connection of one or more substations (drives or I/O stations), it is often necessary in practice to reconfigure an existing network. This becomes necessary, e.g., when new components are to be added to an existing automation line and new participants must be integrated. In addition, “cabling” must be prescribed when the network channels are allocated in a fixed manner to ensure redundancy. The connections between the participants and the hardware side must be noted exactly. Faulty configurations can result in service interruptions with serious consequences, and expensive troubleshooting.